Brush adsorbed, structure

Figure 4.34 Different types of nanoparticle (a) nanosphere stabilised by an adsorbed non-ionic surfactant (b) core-shell nanosphere with a brush shell structure (c) core-shell nanosphere with a loop shell structure (d) core-shell nanocapsule with a brush shell structure.

In a solvent that selectively solubilizes one of the blocks, when the chain adsorbs, the anchor collapses to form a dense layer, while the buoy stretches out to form a brush-like structure. Adsorption in this case is decided by the competition between van der Waals attraction between the anchor and the substrate and repulsive interactions between the buoys. This is referred to as the van der Waals brush regime (37). 

Calculations from SCF theory of the mixed layer structure, and of the interaction potential for a pair of mixed layers as a function of interlayer separation, suggest that the mixed layer has a heterogeneous morphology perpendicular to die interface (Parkinson et al., 2005). This localized segregation arises from the excluded volume interaction between spaced-out casein chains and the dense brush-like layer that was invoked in the simple SCF model to represent the p-lactoglobulin adsorbed monolayer. 

Clearly, the repulsion between the adsorbed PEO chains is significant which forces them to adopt strongly stretched conformations, a brush structure. The degree of... 

Heuberger and co-workers obtained, by using eSFA, a very intriguing result. Their data indicate that there exists a fine structure embedded within the established steric repulsion of PEG in the brush regime (Fig. 15) [159] arising due to restriction of the conformational space of the PEG/water complex, which causes quantisation of the steric force observed in the SFA. The presence of this water-induced restricted conformation space was suggested to have implications in protein adsorption since in order to adsorb a protein induces a local deformation, which necessitates a restriction of the PEG and protein conformational space, which is energetically and kinetically unfavourable [159, 160]. 

There are several ways of forming surface layers of polymer chains, and various solid/polymer systems have been used. The silica/PDMS system is quite convenient since both end-grafted layers with high grafting densities (i.e., brushes) and irreversibly adsorbed layers (i.e., pseudo-brushes) can be formed with controlled molecular characteristics (polymerization index of the tethered chains and surface density), allowing a detailed investigation of the structure and properties of these two different classes of surface anchored polymer layers. 

The internal structure of a Guiselin s pseudo-brush is schematically presented in Fig. 4. Similar arguments in the case of an irreversibly adsorbed layer pre-... 

Amphiphilic diblock copolymers act as a surfactant and stabilize free-standing films. They are assumed to adsorb at the interface by analogy with low-molecular-weight surfactants The hydrophobic part is collapsed at the interfaces and the hydrophilic part is directed towards the film core (Fig. 2a). Investigations of the structure at a single liquid interface (air/water) show that the amphiphilic diblock copolymers present polymer brushes which are anchored by the hydrophobic block at the interface [22, 23], This structure is also assumed at the film surfaces. Fig. 3 shows the disjoining pressure iso-... 

Figure 10. (a) Molecular brushes with poly(methyl methacrylate) side chains were adsorbed on mica and annealed above the glass transition temperature T= 105 °C for 24 h. (b) The undulated structures in higher magnification images demonstrate the tendency of the brush molecules to contraction via the buckling mechanism. The height of the molecules was determined to be 2 nm and the width 16 2 nm. 

The observation that a macromolecular brush gets stretched as the side chains get adsorbed on a flat surface provides a means to stimulate molecular motility by desorption of the brush molecule or a segment of it. If the molecule is in a subsequent period allowed to relax to the adsorbed stretched state it will eventually do a step forward. This is depicted schematically in Figure 28 as a sort of a creep motion. Here, the desorbed state might be characterized as an excited state whose formation requires input of energy. In the case that the structure of the surface and of the molecule favor relaxation into a distinct direction, i.e., in the case of an asymmetric potential, the motion of the molecule can be become directed. 

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